Finally. I tried all of the other suggestions. I could sign in with my own ID, but my husband's ID wouldn't work on either of our computers, which meant it was tied to his ID and not iTunes. I tried deleting, reinstalling folders etc anyway.

Finally using this advice (see the post I replied to) I signed myself out, clicked 'create Apple ID' and went in a couple of pages to where it started asking for information. I then clicked on the dropdown chose Itunes store and 'sign in' and tried again with my husband's id, and it let him sign in and brought him to the veryify payment type screen where I had to fill in all the default payment info again. Once that was done he was now again logged into iTunes. I logged him out and back in to test and it worked, then logged myself back in.

So what was that all about??

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Full step by step for anyone still dealing with this issue

In iTunes from the top left drop down menu choose iTunes Store

Make sure you are logged out from all your accounts (as this addresses the issue of being able to log into some and not others).

Choose 'Create Apple ID'

Follow the first two pages, agree to the T&Cs etc, until you get to the page where it asks you for your email address and password info you'd like to use.

Instead of filling that in, go back up to the top left dropdown box and choose iTunes Store and 'sign in' and try to sign in with the ID you've been struggling with.

For me at that point it signed me in and brought me to the card payment verification page where I had to input and confirm our payment method which I did. Once completed it brought me to the iTunes store logged in as my husband.

I logged him out and back in again through itunes and was able to authorise his ID for my computer (new hard drive so new iTunes installation), and then log him out and me back in. All is working fine now.

I hope this is of some help to others who might be still dealing with this issue.

Had a bit of a setback. The same issue was happening on 2 machines. I assumed when I fixed it on the first that it would fix the ID on both.

When I went back to hubby's laptop he was still having the same issue. I followed the same steps I did above, and it worked, only this time it didn't ask for card verification, it just signed him into the iTunes Store. Logged out and in twice to be sure and it is working. So you may have to re-set all your computers individually by going into 'create apple id' then through the first couple of pages, then sign in.

There seems to be a few different causes of the issue but I really hope this does help some people.

(ps - running Windows 7 on PC, so this isn't just a Windows 8 problem as some have speculated)

This worked perfectly. Ironic enough I was on the phone with Apple Support who had no idea how to fix the issue and was elevating the call to a supervisor when I came across this post and tried while I was on hold. I directed Apple Support to this post so they'll know what to do in the future. Maybe they will give you a credit Jerome. At any rate I know I greatly appreciate it!

chelynnah, Thanks very much this worked perfectly. I'd tried all the other solutions on here (taking about 4 hours in total) and none of them worked but your solution did - Thanks. BTW I'm running Windows 8 and the latest version of iTunes - 11.3.1.8

After following all of the instructions in previous posts...I couldn't get them to work for my mac pro. The most simple solution finally worked. I started safari, "clicked" on the Safari menu (upper left of screen), scrolled to "reset safari" ...problem solved.

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